Valves for the latter use are also known as fill limit vent valves (FLVV). They have a float that is directly or indirectly connected to a sealing arrangement which seals a valve housing vent opening, connected with the environment, for example, when during fueling the fuel level has reached a predetermined height. A problem with this type of valve is that during the operation of the vehicle the float can be lifted by fuel splashing up, and the vent opening of the valve can be sealed. Thereby, due to vaporizing fuel, an internal pressure can build up exerting a force on the sealing arrangement, which in the simplest case is a disk of elastomer material, the force exceeding the weight of the float, such that the vent opening remains closed at least for a certain duration. Thus, the danger exists of the tank being damaged by the internal pressure.
To reduce this danger, among others, two-stage valves are used. In these valves, known, for example, from US 2005/0126633 A1, a sealing arrangement is present, in which initially a smaller opening cross-section is released, which due to the smaller surface upon which the internal pressure can act, requires a lower force expenditure. The internal pressure can be reduced until the weight of the float is sufficient to remove the sealing arrangement from a second, larger opening cross-section that corresponds, for example, approximately to the cross-sectional area of the vent opening. Because the first opening cross-section cannot be selected to be too large, in order to enable the opening of the first stage during greater internal pressures, it takes a relatively long time until the internal pressure is reduced to a value that permits the opening of the second valve stage.